Methods and implantable medical systems that implement exposure modes of therapy that allow for continued operation during exposure to a magnetic disturbance

Abstract

Implantable medical systems enter an exposure mode of operation, either manually via a down linked programming instruction or by automatic detection by the implantable system of exposure to a magnetic disturbance. A controller then determines the appropriate exposure mode by considering various pieces of information including the device type including whether the device has defibrillation capability, pre-exposure mode of therapy including which chambers have been paced, and pre-exposure cardiac activity that is either intrinsic or paced rates. Additional considerations may include determining whether a sensed rate during the exposure mode is physiologic or artificially produced by the magnetic disturbance. When the sensed rate is physiologic, then the controller uses the sensed rate to trigger pacing and otherwise uses asynchronous pacing at a fixed rate.

What is claimed is: 
     
       1. A method for controlling an exposure mode of therapy of an implantable medical device comprising:
 determining whether a sensed heart rate of a patient exceeds a first threshold; 
 when the sensed heart rate does not exceed the first threshold, then selecting a pacing rate for the exposure mode that is equal to the sensed heart rate plus a first adjustment; 
 when the sensed heart rate does exceed the first threshold, determining that the sensed heart rate does not exceed a second threshold that is higher than the first threshold and/or a ventricular pacing percentage does not exceed a pacing percentage threshold; 
 when the sensed heart rate does not exceed the second threshold and/or the ventricular pacing percentage does not exceed the pacing percentage threshold, then selecting the pacing rate for the exposure mode that is equal to the sensed heart rate plus a second adjustment; and 
 at least one of causing an external device to provide an instruction about the exposure mode to the implantable medical device and/or causing the implantable medical device to enter the exposure mode. 
 
     
     
       2. The method of  claim 1 , further comprising when the sensed heart rate does exceed the second threshold and the ventricular pacing percentage does exceed the pacing percentage threshold, then selecting a pacing rate for the exposure mode based on a device type of the implantable medical device. 
     
     
       3. The method of  claim 2 , further comprising:
 determining the device type is other than a cardiac resynchronization therapy device; and setting the pacing rate to a fixed amount higher than the first threshold and lower than the second threshold when the device type is other than a cardiac resynchronization therapy device. 
 
     
     
       4. The method of  claim 3 , further comprising setting a pacing mode to a VOO mode when the device type is other than a cardiac resynchronization therapy device. 
     
     
       5. The method of  claim 2 , further comprising:
 determining the device type is other than a cardiac resynchronization therapy device; and setting the pacing rate to be equal to the heart rate plus the second adjustment when the device type is a cardiac resynchronization therapy device. 
 
     
     
       6. The method of  claim 1 , wherein selecting the pacing rate for the exposure mode when the sensed heart rate does not exceed the second threshold and/or the ventricular pacing percentage does not exceed the pacing percentage threshold comprises selecting the pacing rate for the exposure mode that is equal to the sensed heart rate plus a second adjustment but limited to a specified maximum pacing rate. 
     
     
       7. The method of  claim 1 , further comprising:
 determining a device type of the implantable medical device; and 
 selecting a pacing mode for the exposure mode based at least on the device type. 
 
     
     
       8. The method of  claim 1 , further comprising:
 determining one or more of a device type of the implantable medical device, a pre-exposure pacing mode of the implantable medical device and/or the ventricular pacing percentage; and 
 selecting a pacing mode for the exposure mode based at least on the one or more of the device type of the implantable medical device, the pre-exposure pacing mode of the implantable medical device, and/or the ventricular pacing percentage. 
 
     
     
       9. The method of  claim 8 , wherein the pacing mode for the exposure mode comprises one of an OXO, AOO, VOO and DOO pacing mode. 
     
     
       10. A device for controlling an exposure mode of therapy of an implantable medical device comprising:
 a controller configured to:
 determine whether a sensed heart rate of a patient exceeds a first threshold; 
 when the sensed heart rate does not exceed the first threshold, select a pacing rate for the exposure mode that is equal to the sensed heart rate plus a first adjustment; 
 when the sensed heart rate does exceed the first threshold, determine that the sensed heart rate does not exceed a second threshold that is higher than the first threshold and/or a ventricular pacing percentage does not exceed a pacing percentage threshold; 
 when the sensed heart rate does not exceed the second threshold and/or the ventricular pacing percentage does not exceed the pacing percentage threshold, then select the pacing rate for the exposure mode that is equal to the sensed heart rate plus a second adjustment; and 
 at least one of cause the device to provide an instruction about the exposure mode to the implantable medical device and/or cause the implantable medical device to enter the exposure mode. 
 
 
     
     
       11. The device of  claim 10 , wherein the controller is further configured to determine the sensed heart rate does exceed the second threshold and the ventricular pacing percentage does exceed the pacing percentage threshold and select a pacing rate for the exposure mode based on a device type of the implantable medical device in response to determining the sensed heart rate does exceed the second threshold and the ventricular pacing percentage does exceed the pacing percentage threshold. 
     
     
       12. The device of  claim 11 , wherein the controller is further configured to:
 determine the device type is other than a cardiac resynchronization therapy device; and set the pacing rate to a fixed amount higher than the first threshold and lower than the second threshold when the device type is other than a cardiac resynchronization therapy device. 
 
     
     
       13. The device of  claim 12 , wherein the controller is further configured to set a pacing mode to a VOO mode when the device type is other than a cardiac resynchronization therapy device. 
     
     
       14. The device of  claim 11 , wherein the controller is further configured to:
 determine the device type is other than a cardiac resynchronization therapy device; and 
 set the pacing rate to be equal to the heart rate plus the second adjustment when the device type is a cardiac resynchronization therapy device. 
 
     
     
       15. The device of  claim 10 , wherein the controller is further configured to select the pacing rate for the exposure mode that is equal to the sensed heart rate plus a second adjustment but limited to a specified maximum pacing rate when the sensed heart rate does not exceed the second threshold and/or the ventricular pacing percentage does not exceed the pacing percentage threshold. 
     
     
       16. The device of  claim 10 , wherein the controller is further configured to: determine a device type of the implantable medical device; and
 select a pacing mode for the exposure mode based at least on the device type. 
 
     
     
       17. The device of  claim 10 , wherein the controller is further configured to:
 determine one or more of a device type of the implantable medical device, a pre-exposure pacing mode of the implantable medical device and/or the ventricular pacing percentage; and 
 select a pacing mode for the exposure mode based at least on the one or more of the device type of the implantable medical device, the pre-exposure pacing mode of the implantable medical device, and/or the ventricular pacing percentage. 
 
     
     
       18. The device of  claim 17 , wherein the pacing mode for the exposure mode comprises one of an OXO, AOO, VOO and DOO pacing mode. 
     
     
       19. The device of  claim 10 , wherein the device comprises an external device, the external device further comprising:
 a telemetry component configured to communicate via wireless communication, wherein the controller is further configured to obtain information, including at least the sensed heart rate, from the implantable medical device via wireless communication and provide an instruction about the exposure mode of therapy to the implantable medical device via the wireless communication. 
 
     
     
       20. The device of  claim 10 , wherein the device comprises the implantable medical device, the implantable medical device further comprising:
 a telemetry component configured to communicate via wireless communication, 
 wherein the controller is further configured to select the pacing rate in response to one of a command received via wireless communication to enter the exposure mode or in response to a detected the magnetic disturbance.